A3 LT4

Question 1

Where is the movable electric contact mounted?

Answer 1

On the armature

Question 2

What happens when current flows through the coil?

Answer 2

Armature attracted to coil core

Question 3

What is the basic meter movement used in most commercial analog meters?

Answer 3

D’Arsonval meter

Question 4

What does current flow in the coil of an analog meter produce?

Answer 4

Clockwise torque

Question 5

What is the basis for meters measuring AC and DC currents and voltages, as well as resistance?

Answer 5

D’Arsonval movement

Question 6

Where is the stationary contact mounted?

Answer 6

On the same base as the coil core

Question 7

What happens when the current stops flowing?

Answer 7

Spring causes armature to move away

Question 8

What is the basic construction of the meter movement called?

Answer 8

D’Arsonval meter

Question 9

What is the torque in the coil of an analog meter directly proportional to?

Answer 9

The amount of current flowing in the coil

Question 10

What causes the pointer in an analog meter to oscillate?

Answer 10

Combined action of moving coil and restraining springs

Question 11

What is the purpose of contacts?

Answer 11

Isolate the coil from the current.

Question 12

What is the moving coil in an analog meter made of?

Answer 12

Fine copper wire

Question 13

Why is the instrument movement in a D’Arsonval meter extremely delicate?

Answer 13

Can only handle milliamps or microamps

Question 14

Why is damping necessary in an analog meter?

Answer 14

To suppress oscillation

Question 15

What must be done to release the material attracted to the lifting magnet?

Answer 15

Open the switch to stop current flow

Question 16

What does the current passing through the coils produce?

Answer 16

Magnetic field

Question 17

What is the aluminum frame in an analog meter mounted on?

Answer 17

Shaft pivoted between two jewelled bearings

Question 18

What is a relay?

Answer 18

Electromagnetic switch

Question 19

How does the current flow in the system when the bell button is pressed?

Answer 19

Current starts to flow again

Question 20

What happens as the cycle repeats itself with the bell system?

Answer 20

Armature repeatedly strikes the bell

Question 21

What are motors and generators commonly used for?

Answer 21

Produce mechanical energy from electrical energy

Question 22

How are field poles created in these machines?

Answer 22

Passing a current through coils wound around a magnetic core called the stator

Question 23

What enables the coil in an anoalog meter to move freely?

Answer 23

Jewelled bearings

Question 24

What happens when the current through an undamped analog meter is increased suddenly from 0 to some value A amps?

Answer 24

Pointer oscillates about the value A before coming to rest.

Question 25

What happens when current is passed through a coil?

Answer 25

Attracts a spring-loaded armature

Question 26

What causes the contacts to come together and close the switch?

Answer 26

Current flowing through the coil

Question 27

What controls the magnitude of the current through the field coils?

Answer 27

Field rheostat

Question 28

What is attached to the coil in an analog meter?

Answer 28

Pointer

Question 29

Why is it difficult to read the analog meter quickly and accurately?

Answer 29

Pointer oscillates with every fluctuation of current.

Question 30

How are magnetic relays used?

Answer 30

Small current controls large current

Question 31

Why is the flux density of the field varied in these machines?

Answer 31

To control speed, torque, and voltage

Question 32

How is the current conducted to and from the coil in an analog meter?

Answer 32

Spiral springs

Question 33

How does the deadbeat instrument behave?

Answer 33

pointer moves across smoothly without oscillation

Question 34

What is similar about the operation of a bell and a buzzer?

Answer 34

Same basic operation.

Question 35

What keeps the coil in the rest position when no current flows in an analog meter?

Answer 35

Spiral springs

Question 36

What happens when the armature moves toward the coils?

Answer 36

Strikes the bell

Question 37

How is current indicated in the coil of an analog meter?

Answer 37

By the attached pointer on a calibrated scale

Question 38

What is the function of the two springs in the coil of an analog meter?

Answer 38

They conduct current to the coil and restrain its movement

Question 39

What does the D'Arsonval movement require to measure AC values?

Answer 39

Built-in rectifier

Question 40

What happens to the core when a current is passed through the coil?

Answer 40

Becomes magnetized and poles are formed

Question 41

What happens when the current stops flowing in a core with low retentivity?

Answer 41

Field collapses and material is released

Question 42

What pulls the armature away from the coils?

Answer 42

Spring

Question 43

What two principles does the operation of an analog meter depend on?

Answer 43

Coil becoming an electromagnet; Like poles repel, unlike attract

Question 44

What does the D'Arsonval movement require to measure resistance?

Answer 44

Internal battery

Question 45

What is the difference between a buzzer and a bell in terms of the armature?

Answer 45

No bell to strike for the buzzer

Question 46

What do generators use to produce electrical energy from mechanical energy?

Answer 46

Magnetoelectric effect

Question 47

What are the magnetic poles required for generators and motors called?

Answer 47

Field poles

Question 48

When does the pointer stop moving in the coil in an analog meter?

Answer 48

When the torques balance each other out

Question 49

What is the maximum current the coils in a D'Arsonval meter movement can handle?

Answer 49

About 50 mA